Method for removing native oxide and associated residue from a substrate

ABSTRACT

Native oxides and associated residue are removed from surfaces of a substrate by sequentially performing two plasma cleaning processes on the substrate in a single processing chamber. The first plasma cleaning process removes native oxide formed on a substrate surface by generating a cleaning plasma from a mixture of ammonia (NH 3 ) and nitrogen trifluoride (NF 3 ) gases, condensing products of the cleaning plasma on the native oxide to form a thin film that contains ammonium hexafluorosilicate ((NH 4 ) 2 SiF 6 ), and subliming the thin film off of the substrate surface. The second plasma cleaning process removes remaining residues of the thin film by generating a second cleaning plasma from nitrogen trifluoride gas. Products of the second cleaning plasma react with a few angstroms of the bare silicon present on the surface, forming silicon tetrafluoride (SiF 4 ) and lifting off residues of the thin film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Continuing application Ser.No. 13/906,543, filed May 31, 2013 (Attorney Docket No.APPM/015849USC1), which is a continuation of U.S. Pat. No. 8,455,352(application Ser. No. 13/480,091), filed May 24, 2012, each of which isherein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate generally to semiconductorsubstrate processing and, more particularly, to systems and methods forcleaning native oxide and associated residue from a substrate.

2. Description of the Related Art

In the microfabrication of integrated circuits and other devices,electrical interconnect features, such as contacts, vias, and lines, arecommonly constructed on a substrate using high aspect ratio aperturesformed in a dielectric material. The presence of native oxides and othercontaminants such as etch residue within these small apertures is highlyundesirable, contributing to void formation during subsequentmetallization of the aperture and increasing the electrical resistanceof the interconnect feature.

A native oxide typically forms when a substrate surface, such as a baresilicon surface, is exposed to oxygen and water. Oxygen exposure occurswhen substrates are moved between processing chambers at atmospheric orambient conditions, or when a small amount of oxygen remains in aprocessing chamber. In addition, native oxides may result fromcontamination during etching processes. Native oxide films are usuallyvery thin, for example between 5-20 angstroms, but thick enough to causedifficulties in subsequent fabrication processes. Therefore, a nativeoxide layer is typically undesirable and needs to be removed prior tosubsequent fabrication processes.

For example, a particular problem arises when native silicon oxide filmsare formed on exposed silicon containing layers, especially duringprocessing of metal oxide silicon field effect transistor (MOSFET)structures. Silicon oxide films are electrically insulating and areundesirable at interfaces with contact electrodes or interconnectingelectrical pathways because they cause high electrical contactresistance. In MOSFET structures, the electrodes and interconnectingpathways include silicide layers formed by depositing a refractory metalon bare silicon and annealing the metal to produce a metal silicidelayer. Native silicon oxide films at the interface between the siliconsubstrate and the deposited metal reduce the compositional uniformity ofthe silicide layer by impeding the diffusional chemical reaction thatforms the metal silicide during anneal. This results in lower substrateyields and increased failure rates due to overheating at the electricalcontacts. The native silicon oxide film can also prevent adhesion oflayers which are subsequently deposited on the substrate.

Various techniques are known for removing native oxides from a surfaceprior to metallization, but generally have one or more drawbacks.Sputter etch processes have been used to reduce contaminants, but aregenerally only effective in large features or in small features havingaspect ratios less than about 4:1. In addition, sputter etch processescan damage delicate silicon layers by physical bombardment. Wet etchprocesses utilizing hydrofluoric acid are used to remove native oxides,but are less effective in smaller features with aspect ratios exceeding4:1. This is because the aqueous solution has difficulty penetrating andbeing removed from vias, contacts, or other small features formed on thesubstrate surface, resulting in incomplete removal of the native oxidefilm and subsequent contamination issues. Also used to remove nativeoxides is a cleaning plasma that is generated from a mixture of ammoniaand nitrogen trifluoride gases. When condensed on a substrate surfacewith a native silicon oxide, the products of the cleaning plasma form athin film, containing ammonium hexafluorosilicate, from the nativeoxide. The film can be subsequently heated and sublimed off of thesubstrate. In high aspect ratio features, however, the thin film may notcompletely sublime, leaving an unwanted residue on the substrate.Furthermore, water generated in the formation of the thin film mayproduce additional native oxide on the substrate.

Accordingly, there is a need in the art for methods of removing nativeoxides and associated residue from a substrate that does not have thedisadvantages outlined above.

SUMMARY OF THE INVENTION

One or more embodiments of the present invention provide methods forremoving native oxides and associated residue by sequentially performingtwo plasma cleaning processes on a substrate in a single processingchamber. The first plasma cleaning process removes native oxide formedon a substrate surface by generating a cleaning plasma from a mixture ofammonia (NH₃) and nitrogen trifluoride (NF₃) gases, condensing productsof the cleaning plasma on the native oxide to form a thin film thatcontains ammonium hexafluorosilicate ((NH₄)₂SiF₆), and subliming thethin film off of the substrate surface. The second plasma cleaningprocess removes remaining residues of the thin film by generating asecond cleaning plasma from nitrogen trifluoride gas. Products of thesecond cleaning plasma react with a few angstroms of the bare siliconpresent on the surface, forming silicon tetrafluoride (SiF₄) and liftingoff residues of the thin film.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIGS. 1A-1F are schematic cross-sectional views of a substrate surfacetreated according to embodiments of the invention.

FIG. 2 is a schematic cross-sectional view of a high-aspect featureformed on a substrate that includes the substrate surface illustrated inFIG. 1F.

FIG. 3 is a schematic cross-sectional view of a processing chamberconfigured to perform a two-step plasma cleaning process according toone or more embodiments of the invention.

FIG. 4 is a flowchart of method steps for processing a substrate in aprocessing chamber, according to one or more embodiments of the presentinvention.

FIG. 5 is a schematic plan view diagram of an exemplary multi-chamberprocessing system configured to perform a high-frequency, hydrogen-basedplasma process on a substrate, according to one or more embodiments ofthe invention.

FIG. 6 is a flowchart of method steps for processing a substrate in amulti-chamber processing system, according to one or more embodiments ofthe present invention.

For clarity, identical reference numbers have been used, whereapplicable, to designate identical elements that are common betweenfigures. It is contemplated that features of one embodiment may beincorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

FIGS. 1A-1F are schematic cross-sectional views of a substrate surfacetreated according to embodiments of the invention. Substrate 100 may bea 200 or 300 mm silicon wafer, or any other substrate used to fabricatemicroelectronic devices and the like. Substrate 100 includes a bulkregion 130 that may be a silicon-containing underlayer or may be theactual underlying bulk portion of substrate 100. As shown in FIG. 1A,substrate 100 includes a nitride layer 120 with an opening 102 formedtherein to expose a surface 131 of bulk region 130. Nitride layer 120may comprise silicon nitride (Si₃N₄) and/or other durable maskingmaterials, and is deposited on bulk region 130 to protect bulk region130 during oxide deposition and other fabrication processes. A nativeoxide layer 101 is formed in opening 102 of nitride layer 120 due to theexposure of surface 131 of bulk region 130 to either atmosphere or toone or more fabrication processes that cause native oxide layer 101 toform, such as wet processes.

In FIG. 1B, substrate 100 is illustrated after undergoing a first plasmacleaning process, according to embodiments of the invention. One suchembodiment is described below in conjunction with FIG. 4. As shown,native oxide layer 101 has been removed, leaving surface 131 of bulkregion 130 exposed. However, residues 140 and regions 133 of nativeoxide may be scattered across surface 131. Residues 140 may be remainderportions of an ammonium hexafluorosilicate ((NH₄)₂SiF₆) containing filmthat were not completely sublimed from surface 131 during the firstplasma cleaning process. Regions 133 may be very thin regions of nativeoxide, and may be formed on surface 131 after the first plasma cleaningprocess, since water vapor is produced as a byproduct of the firstplasma cleaning process, or may be residual portions of native oxidelayer 101 that were not completely removed.

In FIG. 1C, substrate 100 is illustrated after undergoing a secondplasma cleaning process, according to embodiments of the invention. Onesuch embodiment is described below in conjunction with FIG. 4. As shown,residues 140 and regions 133 of native oxide have been removed. Becausethe second plasma cleaning process is performed in a vacuum chamber,surface 131 of bulk region 130 has no significant exposure to oxygen,and therefore remains free of native oxide.

In FIG. 1D substrate 100 is illustrated after a metal layer 190 has beendeposited on substrate 100. Metal layer 190 may be deposited by anytechnically feasible technique, including physical vapor deposition(PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD),and the like. In one embodiment, metal layer 190 includes a CVD cobaltlayer, to facilitate the formation of a silicide layer on surface 131.In other embodiments, metal layer 190 includes one or more of tungsten,titanium, and nickel. Because the first and second plasma cleaningprocesses can be performed in one chamber of a multi-chamber processingsystem and metal layer 190 can be deposited in another chamber of thesame multi-chamber processing system, metal layer 190 can be depositedon substrate 100 without exposing substrate 100 to atmosphere.Consequently, surface 131 comprises an extremely clean surface free ofnative oxide and other residues, and a high quality silicide interfacecan be formed thereon.

In FIG. 1E, substrate 100 is illustrated after a thermal anneal processhas formed a silicide layer 135 from metal layer 190 and bulk region130. In some embodiments, described below in conjunction with FIG. 6,the thermal anneal process forming silicide layer 135 is performed in achamber of the multi-chamber processing system that is also used toperform the first and second plasma cleaning processes and thedeposition of metal layer 190.

In FIG. 1F, substrate 100 is illustrated after metal layer 190 has beenremoved from substrate 100, leaving metal silicide layer 135 exposed inopening 102.

In some embodiments, opening 102, surface 131, and nitride layer 120 maybe disposed on a sidewall of a high aspect ratio feature formed onsubstrate 100. For example, surface 131 may be configured as an elementof a vertical contact formed adjacent a very high aspect ratio trench,via, or other aperture. One such embodiment is illustrated in FIG. 2.FIG. 2 is a schematic cross-sectional view of a high aspect ratiofeature 200 formed on a substrate that includes the substrate surfaceillustrated in FIG. 1F. High aspect ratio feature 200 may be a trench,via, or other aperture formed on a surface of a substrate 250 as part ofthe fabrication process of a microelectronic device. For example, highaspect ratio feature 200 may comprise a portion of a vertical contact.The ratio of depth 201 to width 202 of high aspect ratio feature 200 maybe greater than 10:1 or, in some embodiments, greater than 100:1.Consequently, complete sublimation of an ammonium hexafluorosilicatethin film during a plasma cleaning process is unreliable, leavingunwanted residue that can deleteriously affect the quality ofsubsequently deposited metal layers. According to one or moreembodiments of the invention, a two-step plasma cleaning processaddresses this issue.

FIG. 3 is a schematic cross-sectional view of a processing chamber 300configured to perform a two-step plasma cleaning process according toone or more embodiments of the invention. Processing chamber 300includes a lid assembly 320 disposed at an upper end of a chamber body312, and a support assembly 315 at least partially disposed withinchamber body 312. Processing chamber 300 also includes a remote plasmagenerator 340. Exemplary remote plasma generators are available fromvendors such as MKS Instruments, Inc., and Advanced Energy Industries,Inc. Processing chamber 300 and the associated hardware are preferablyformed from one or more process-compatible materials, for example,aluminum, anodized aluminum, nickel plated aluminum, nickel platedaluminum 6061-T6, stainless steel, as well as combinations and alloysthereof.

Support assembly 315 is disposed within chamber body 312. Supportassembly 315 is raised and lowered by a shaft 314, which is enclosed bya bellows 333, and includes a substrate support member 310. Chamber body312 includes a slit valve opening 360 formed in a sidewall thereof toprovide access to the interior of processing chamber 300. In oneembodiment, a substrate 100 may be transported in and out of processingchamber 300 through slit valve opening 360 to an adjacent transferchamber and/or load-lock chamber (not shown), or another chamber withina cluster tool. Exemplary cluster tools include but are not limited tothe PRODUCER®, CENTURA®, ENDURA®, and ENDURA® SL platforms, availablefrom Applied Materials, Inc., located in Santa Clara, Calif.

Chamber body 312 also includes channels 313 formed therein for flowing aheat transfer fluid therethrough. The heat transfer fluid may be aheating fluid or a coolant and is used to control the temperature ofchamber body 312 during processing and substrate transfer. Thetemperature of chamber body 312 is important to prevent unwantedcondensation of process gas or byproducts on the chamber walls.Exemplary heat transfer fluids include water, ethylene glycol, or amixture thereof.

Chamber body 312 further includes a liner 334 that surrounds supportassembly 315 and is removable for servicing and cleaning. Liner 334 maybe made of a metal such as aluminum, a ceramic material, or any othermaterial or materials that are compatible for use during the process ofsubstrates in processing chamber 300. Liner 334 typically includes oneor more apertures 335 and a pumping channel 329 formed therein that isin fluid communication with a vacuum system. Apertures 335 provide aflow path for gases into pumping channel 329, and the pumping channelprovides a flow path through liner 334 so the gases can exit processingchamber 300.

Processing chamber 300 further includes a vacuum pump 325 and a throttlevalve 327 to regulate flow of gases within processing chamber 300.Vacuum pump 325 is coupled to a vacuum port 331 disposed on chamber body312, and is in fluid communication with pumping channel 329 formedwithin liner 334. Vacuum pump 325 and chamber body 312 are selectivelyisolated by throttle valve 327 to regulate flow of the gases withinprocessing chamber 300.

Lid assembly 320 contains a number of components stacked together. Forexample, lid assembly 320 contains a lid rim 311, gas delivery assembly305, and top plate 350. Lid rim 311 is designed to hold the weight ofthe components making up lid assembly 320 and is coupled to an uppersurface of chamber body 312 to provide access to the internal chambercomponents. Gas delivery assembly 305 is coupled to an upper surface oflid rim 311 and is arranged to make minimum thermal contact therewith.The components of lid assembly 320 are preferably constructed of amaterial having a high thermal conductivity and low thermal resistance,such as an aluminum alloy with a highly finished surface, for example.Preferably, the thermal resistance of the components is less than about5×10−4 m² K/W.

Gas delivery assembly 305 may comprise a gas distribution plate 326 orshowerhead. A gas supply panel (not shown) is typically used to providethe one or more gases to processing chamber 300. The particular gas orgases that are used depend upon the processes to be performed withinprocessing chamber 300. To facilitate the plasma cleaning processes asdescribed herein, such process gases include ammonia, nitrogentrifluoride, and one or more carrier and purge gases, and other suitablegases. Typically, the process gases are introduced to processing chamber300 into lid assembly 320 and then into chamber body 312 through gasdelivery assembly 305.

In some embodiments, instead of using remote plasma generator 340, lidassembly 320 may include an electrode 341 to generate a plasma ofreactive species within lid assembly 320, instead of receiving. In suchan embodiment, electrode 341 is supported on top plate 350 and iselectrically isolated therefrom, for example with an isolator ring (notshown). Also in such an embodiment, electrode 341 is coupled to a powersupply 343 and gas delivery assembly 305 is connected to ground.Accordingly, a plasma of the one or more process gases can be struck inthe volume formed between electrode 341 and gas delivery assembly 305.Thus, the plasma is well confined or contained within lid assembly 320.

Any power source may be used in processing chamber 300 that is capableof activating the gases into reactive species and maintaining the plasmaof reactive species, whether remote plasma generator 340 or electrode341 is used to generare a desired plasma. For example, radio frequency(RF), direct current (DC), alternating current (AC), or microwave (MW)based power discharge techniques may be used. Plasma activation may alsobe generated by a thermally based technique, a gas breakdown technique,a high intensity light source (e.g., UV energy), or exposure to an x-raysource.

Gas delivery assembly 305 may be heated depending on the process gasesand operations to be performed within processing chamber 300. In oneembodiment, a heating element 370, such as a resistive heater, iscoupled to gas delivery assembly 305 and regulates the temperature ofgas delivery assembly 305. In the embodiment illustrated in FIG. 3, thebottom surface of gas delivery assembly 305 is substantially parallel tothe top surface of substrate support member 310. In other embodiments,the bottom surface of gas delivery assembly 305 may be dome-shaped orotherwise configured in order to optimize gas flow and heating of asubstrate in processing chamber 300.

Processing chamber 300 is particularly useful for performing plasmacleaning processes as described herein, since heating and cooling of thesubstrate surface without breaking vacuum is required.

FIG. 4 is a flowchart of method steps for processing a substrate in aprocessing chamber, according to one or more embodiments of the presentinvention. Method 400 includes a two-step plasma cleaning process forremoving native oxides and residues associated with the oxide removalprocess, i.e., ammonium hexafluorosilicate. Although the method stepsare described in conjunction with processing chamber 300 in FIG. 3, itis understood that any processing chamber configured to perform themethod steps falls within the scope of the invention.

As shown, method 400 begins at step 401, in which a substrate, such assubstrate 100 illustrated in FIG. 1A, is positioned on substrate supportmember 310 and controlled to a desired temperature. Substrate 100includes native oxide layer 101 disposed in opening 102 of nitride layer120, and is placed into chamber body 312 through slit valve opening 360and is disposed on the upper surface of support member 310. Supportmember 310 then lifts substrate 100 to a processing position withinchamber body 312 and cools substrate 100 to a temperature of below about50° C. or less by passing a coolant through fluid channels therein. Insome embodiments, substrate 100 is cooled to a higher temperature than50° C. in step 401, but no greater than 70° C. This is because asubstrate temperature of 75° C. or higher during step 403 (describedbelow) may result in the unwanted sublimation of solid byproducts.Chamber body 312 is preferably heated to a temperature within a rangefrom about 50° C. to about 80° C. by passing a heat transfer mediumthrough the channels 313.

In step 402, a first cleaning plasma is generated, either remotely byremote plasma generator 340 or by power supply 343 coupled to electrode341. First, an etching gas mixture is introduced into remote plasmagenerator 340 or into processing chamber 300, where the gas mixturecomprises nitrogen trifluoride (NF₃) and ammonia (NH₃) and has anNH₃/NF₃ molar ratio of about 5 or greater. The amount of each gasintroduced is variable and may be adjusted to accommodate, for example,the thickness of native oxide layer 101 to be removed, the geometry ofsubstrate 100 and features thereon to be cleaned, the volume capacity ofthe plasma, and the volume capacity of chamber body 312. Next, plasma isgenerated, and plasma energy dissociates the ammonia and nitrogentrifluoride gases into reactive species that combine to form reactivegases, such as ammonium fluoride (NH₄F) and/or ammonium hydrogenfluoride (NH₄F HF). The reactive gases flows through gas deliveryassembly 305 via holes 326A of gas distribution plate 326 to react withthe native oxide layer 101 on substrate 100. In some embodiments, thegas mixture includes one or more carrier gases, which may be introducedprior to striking plasma.

In step 403, products of the first cleaning plasma condense ontosubstrate 100 to form a thin film. Specifically, the thin film includesammonium hexafluorosilicate ((NH₄)₂SiF₆), which is formed in part fromsilicon oxide (SiO_(x)) in native oxide layer 101. In addition, gaseouswater are produced and are removed from processing chamber 300 by vacuumpump 325. It is noted that the temperature of substrate 100 ismaintained at a temperature of 70° C. or below during step 403, and insome embodiments 50° C. or less, to prevent sublimation of the thinfilm. For example, in one embodiment, the temperature of support member310 is controlled to a temperature of about 35-40° C. so that thetemperature of substrate 100 is maintained below about 50° C. or belowduring step 403. It is further noted that the process taking place instep 403 has a high selectivity of etching silicon oxide to siliconnitride, e.g., a selectivity of about 9. Consequently, native oxidelayer 101 can be removed while largely preserving nitride layer 120.

In step 404, substrate 100 is heated within processing chamber 300 to anelevated temperature to remove the thin film of ammoniumhexafluorosilicate from surface 131 of substrate 100. To that end,support member 310 is elevated to an anneal position in close proximityto heated gas distribution plate 326. Heat radiated from gasdistribution plate 326 may sublime the thin film of ammoniumhexafluorosilicate into volatile compounds, such as silicontetrafluoride, ammonia, and hydrogen fluoride. These volatile productsare then removed from processing chamber 300 by vacuum pump 325. Thethin film may be sublimed and removed from substrate 100 when substrate100 is heated to a temperature of about 100° C. or greater. After thesublimation of the ammonium hexafluorosilicate thin film formed in step403, virtually all of native oxide layer 101 is removed, as illustratedin FIG. 1B. However, depending on the geometry and aspect ratio of thefeatures on which native oxide layer 101 is formed, some residue 140 ofthe ammonium hexafluorosilicate thin film may still be present onsurface 131 of substrate 100. In addition, due to the production ofwater vapor in step 403, small regions 133 of native oxide may alsostill be present on surface 131.

In step 405, a second cleaning plasma is generated, either remotely byremote plasma generator 340 or by power supply 343 coupled to electrode341. The second cleaning plasma generated in step 405 differs from thefirst cleaning plasma generated in step 403 in a number of ways. (1) Thegas mixture used includes nitrogen trifluoride but does not includeammonia. (2) The flow rate of the nitrogen trifluoride in step 405 issignificantly greater than in step 403. For example, in an embodiment inwhich processing chamber 300 is configured for a 300 mm diameter siliconwafer, in step 403 the flow rate of nitrogen trifluoride is generallyless than or equal to about 50 sccm. In contrast, in step 405 the flowrate of nitrogen trifluoride is equal to or greater than about 100 sccm,and in some embodiments as high as 500 sccm. It is believed that thehigh nitrogen trifluoride flow rate provides superior selectivity ofsilicon-containing materials, such as polysilicon, over silicon nitride.Consequently, performing the plasma cleaning process of step 405 inaddition to the plasma cleaning process of step 403 does notsubstantially erode nitride layer 120, which is highly desirable. Thisis because nitride layer 120 is a protection layer used to preventsilicide formation in unwanted regions of substrate 100. (3) Theplasma-generating power used in step 405 is significantly higher thanthe plasma-generating power used in step 403. For example, in theembodiment in which processing chamber 300 is configured for a 300 mmdiameter silicon wafer, in step 403 the plasma-generating power isgenerally less than or equal to about 30 to 50 W. In contrast, in step405 the plasma-generating power is equal to or greater than about 350 W,and in some embodiments as high as 500 W. The minimum 350 W is desirableto enable etching of silicon from surface 131. (4) The frequency of RFpower used to generate the plasma in step 403 (less than or equal to 100kHz), is significantly lower than the frequency of RF power used in step405 (equal to or greater than 350 kHz). (5) The temperature of substrate100 is maintained above 100° C. in the second plasma clean step of step405, which helps to remove reaction by-products.

In step 406, substrate 100 is exposed to the second cleaning plasmagenerated in step 405. It is noted that the second plasma cleaningprocess performed in step 405 removes a very small amount of silicon,for example 10 Å or less, and therefore preserves most of bulk region130 of substrate 100. However, the removal of this small quantity ofsilicon from surface 131 also removes the small regions 133 of nativeoxide and lifts off residue 140. In this way, an oxide-free andresidue-free surface 131 is formed on substrate 100. It is noted thatsubstrate 100 may be a vertical side contact in a very narrow feature,for example as narrow as 20 nm or less, so that residue is difficult toremove. However, the second plasma cleaning process described in steps405 and 406 can remove such resides. It is further noted that saidsecond plasma cleaning process provides good selectivity of silicon tosilicon nitride and silicon oxide, thereby preserving nitride layer 120and other features formed on substrate 100 while etching surface 131.Generally, the second plasma cleaning process described herein has anetch rate of essentially zero for silicon nitride and silicon oxide, anda small but finite etch rate for silicon, e.g., 2 to 4 Å/sec.

FIG. 5 is a schematic plan view diagram of an exemplary multi-chamberprocessing system 500 configured to perform a two-step plasma cleaningprocess on substrates 530, according to one or more embodiments of theinvention. Multi-chamber processing system 500 includes one or more loadlock chambers 502, 504 for transferring substrates 530 into and out ofthe vacuum portion of multi-chamber processing system 500. Consequently,load lock chambers 502, 504 can be pumped down to introduce substratesinto multi-chamber processing system 500 for processing under vacuum. Afirst robot 510 transfers substrates 530 between load lock chambers 502and 504, transfer chambers 522 and 524, and a first set of one or moreprocessing chambers 512 and 514. A second robot 520 transfers substrates530 between transfer chambers 522 and 524 and processing chambers 532,534, 536, 538.

One or both of processing chambers 512 and 514 may be configured toperform a two-step plasma cleaning process, according to embodiments ofthe invention described herein, when substrates 530 include native oxidelayer 101 as described with reference to substrate 100. The transferchambers 522, 524 can be used to maintain ultrahigh vacuum conditionswhile substrates are transferred within multi-chamber processing system500. Processing chambers 532, 534, 536, 538 are configured to performvarious substrate-processing operations including cyclical layerdeposition (CLD), atomic layer deposition (ALD), chemical vapordeposition (CVD), physical vapor deposition (PVD), and the like. In oneembodiment, one or more of processing chambers 532, 534, 536, 538 areconfigured to deposit a cobalt stack comprising a plurality ofplasma-treated cobalt layers. Processing chambers suitable fordepositing cobalt layers are conventionally known.

FIG. 6 is a flowchart of method steps for processing a substrate in amulti-chamber processing system, according to one or more embodiments ofthe present invention. Method 600 enables the removal of native oxidelayers and other contaminants from one or more apertures formed on asubstrate. Furthermore, method 600 enables the deposition of barrierlayers, seed layers, and/or other metallization layers in said aperturesimmediately after the removal of the metal oxide layer and prior to anyexposure of the apertures to atmospheric conditions. Consequently, theone or more metal deposition processes are performed on oxide-free metalsurfaces. Although the method steps are described in conjunction withmulti-chamber processing system 600 in FIG. 6, is is understand that anymulti-chamber processing system 600 configured to perform the methodsteps is within the scope of the invention.

As shown, method 600 begins at step 601, in which a substrate 530 istransferred from one of load lock chambers 502, 504 to one of processingchambers 512 and 514.

In step 602, substrate 530 undergoes the two-step plasma cleaningprocess as described above in conjunction with FIG. 3 and illustratedwith reference to FIGS. 1A-1F and FIG. 2. The two-step plasma cleaningprocess removes native oxide layers and contamination from aperturesformed on substrate 530.

In step 603, substrate 530 is transferred by first robot 510 and secondrobot 520 to one or more of processing chambers 532, 534, 536, or 538.

In step 604, substrate 530 undergoes one or more metal depositionprocesses, such as a barrier layer deposition, a seed layer deposition,etc. Because substrate 530 has not been exposed to atmosphere since thetwo-step plasma cleaning process of step 602, the metal depositionprocesses of step 604 are performed on extremely clean surfaces.

In some embodiments, a CVD cobalt deposition process is performed onsubstrate 530 in step 604. In one such embodiment, a cobalt stackcomprising a plurality of plasma-treated cobalt layers is formed on theclean and oxide-free surfaces produced on substrate 530 in step 602. Forexample, each of the cobalt layers may be deposited from a depositiongas containing a cobalt source gas and hydrogen gas during a thermal CVDprocess. The substrate may be heated to a temperature between about 50°C. and about 400° C. during the thermal CVD process.

In one example embodiment, the cobalt source gas includes dicobalthexacarbonyl butylacetylene (CCTBA). Each of the cobalt layers formedmay be exposed to the plasma to form plasma-treated cobalt layers duringa plasma treatment process. The plasma is generally a reducing plasmaand may contain or be formed of a reagent, such as ammonia (NH₃),hydrogen (H₂), hydrazine (N₂H₄), diazene (N₂H₂), an ammonia/hydrogenmixture, derivatives thereof, or combinations thereof. In some examples,each cobalt layer may be exposed to the hydrogen plasma for a timeperiod within a range from about 10 seconds to about 180 seconds duringthe plasma treatment process after each cycle of the thermal CVDdeposition process. In some embodiments, a thermal anneal process isperformed on substrate 530 after the deposition of the stack ofplasma-treated cobalt layers. In this way, a cobalt silicide may beadvantageously formed on surfaces of substrate 530 in a singlemulti-chamber processing system.

In step 605, substrate 530 is transferred back to one of load lockchambers 502 or 504.

In summation, one or more embodiments of the present invention providemethods for removing native oxides and associated residue bysequentially performing two plasma cleaning processes on a substrate ina single processing chamber. Advantages of such embodiments include theformation of extremely clean, oxide-free surfaces, even when suchsurfaces are disposed on high aspect ratio features. In addition, verylittle silicon is removed in forming the clean surfaces, and, due to thehigh selectivity of the plasma cleaning processes over silicon nitride,very little silicon nitride is removed as well. Furthermore, theabove-described cleaning process and the formation of a high qualitymetal silicide can be advantageously performed on a single multi-chamberprocessing system.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

We claim:
 1. A method of processing a substrate disposed in a processingchamber, the method comprising: maintaining a substrate disposed in aprocessing chamber at a temperature less than about 75 degrees Celsius,the substrate having a silicon containing layer exposed through anopening in a nitride layer; and subliming a thin film formed on aportion of the silicon containing layer exposed through the opening inthe nitride layer.
 2. The method of claim 1, further comprising:generating a first cleaning plasma from a first gas mixture with a firstplasma-generating power to form reactive cleaning gases; and forming thethin film on the portion of the silicon containing layer from thereactive cleaning gases and the oxides on the silicon containing layer.3. The method of claim 2, wherein the first gas mixture comprisesnitrogen trifluoride (NF₃) and ammonia (NH₃) and has an NH₃/NF₃ molarratio of about 5 or greater.
 4. The method of claim 3, furthercomprising: adjusting the NH₃/NF₃ molar ratio based on one or more of athickness of the oxides present on the silicon containing layer, afeature or geometry of the substrate, a volume capacity of the plasma,and a volume capacity of the processing chamber.
 5. The method of claim3, wherein the first gas mixture is formed by introducing nitrogentrifluoride into the processing chamber at a first flow rate and thesecond gas mixture is formed by introducing nitrogen trifluoride intothe processing chamber at a second flow rate, the second flow rate beinggreater than the first flow rate.
 6. The method of claim 1, whereinsubliming the thin film comprises: heating the substrate to a secondtemperature greater than 80 degrees Celsius to remove the thin film fromthe surface.
 7. The method of claim 1, further comprising: generating asecond cleaning plasma in the processing chamber from a second gasmixture with a second plasma-generating power greater than the firstplasma-generating power; and exposing the surface of the substrate toproducts of the second cleaning plasma while maintaining the substrateat the second temperature.
 8. The method of claim 7, wherein the secondgas mixture comprises nitrogen trifluoride (NF₃).
 9. The method of claim1, further comprising: transferring the substrate under vacuum from theprocessing chamber to a second chamber in a multi-chamber processingsystem; and depositing a metal film on the surface of the substrate inthe second chamber.
 10. The method of claim 9, wherein depositing themetal film comprises performing chemical vapor deposition process. 11.The method of claim 9, wherein the metal film comprises a cobalt (Co)containing metal.
 12. The method of claim 9, further comprising, withoutremoving the substrate from the multi-chamber processing system,thermally annealing the metal film.
 13. The method of claim 9, whereindepositing the metal film comprises: depositing a cobalt layer during adeposition process; exposing the cobalt layer to a plasma to form aplasma-treated cobalt layer during a plasma process; and repeating thedeposition process and the plasma process to form a cobalt stackcomprising a plurality of plasma-treated cobalt layers.